1. Field of the Invention
The present invention relates generally to seals and, more particularly, to lip-type seals having increased contact force at the interface of the seal and the component it contacts in sealing a first area from a second area.
2. State of the Art
Seals are conventionally used in maintaining a substance, such as a fluid or gas, located in one area or zone from escaping to another area or zone while allowing relative movement of two or more mechanical components with one of the mechanical components traversing through both areas or zones. Such seals may also be used in keeping contaminants, such as dirt, dust or other particulate-type materials, from entering into a specified area or zone. For example, it may be desirable to maintain a lubricant in a specified area or zone while keeping dust or other particulates from entering into the same zone and contaminating the lubricant.
As will be appreciated by those of ordinary skill in the art, the ability to maintain adequate lubrication between two relatively movable machine components, as well as the ability to limit contaminants from entering between the two relatively movable machine components, greatly enhances the working efficiency of the machine components and also greatly reduces wear of such components, thereby increasing the usable life thereof.
Referring to FIG. 1A, a cross-sectional view of an exemplary prior art lip-type seal 10 is shown. The seal 10 includes a body portion 12 and a flared lip portion 14. As shown in FIG. 1B, an external cornice 16 of the flared lip portion 14 is configured to act as a contact surface in forming a seal between two relatively movable machine components 18 and 20. In the exemplary embodiment shown, the seal 10 is configured to maintain a volume of fluid 22 in a zone 24 located between the two relatively movable machine components 18 and 20.
The two relatively movable machine components 18 and 20 may be representative of various devices. For example, the first machine component 18 may be a shaft of a hydraulic cylinder wherein the first machine component 18 reciprocates axially relative to the second machine component 20. Another example may include a bearing assembly wherein the first machine component 18 rotates or moves radially relative the second machine component 20. Numerous other devices may incorporate a seal 10, with most configurations generally including the basic motions of relative rotation and/or relative axial movement between the machine components 18 and 20.
In the case wherein the first machine component 18 moves axially relative to the second machine component 20, for example, it may be desirable to pierce a fluid film (not shown) which develops on the surface of the first machine component 18 in order to provide an effective seal between the two machine components 18 and 20. Such may be accomplished by providing a force at the contact surface of the seal 10 (e.g., the cornice 16) which is sufficient to break the surface tension of the fluid film. Due to conventional tooling and manufacturing limitations, the cornice 16 of the lip portion 14 of the seal 10 conventionally exhibits a radius which acts to distribute any force applied to surface of the first machine component 18 over a larger area by increasing the area of contact therebetween. If a given contact force is distributed over a greater area of contact between the cornice 16 and the first machine component 18, it becomes more difficult to effectively pierce the fluid film formed on the first machine component 18.
Furthermore, while it might seem desirable to provide a cornice 16 with a very small radius (e.g., approaching a point contact) various problems prevent the use of a small radius or pointed cornice. For example, as noted before, due to conventional tooling and manufacturing constraints, it becomes difficult to provide a cornice 16 or contact surface with a sufficiently small radius, particularly in large-scale production where accurate reproducibility of parts is required. For example, it is believed that, due to conventional tooling constraints, it is difficult to consistently and accurately reproduce the cornice 16 or similar contact surface with a radius less than approximately 4 mils (0.004 inch) in large-scale production.
Additionally, in an effort to resist undue deformation of the lip 14 and cornice 16 under loaded conditions, in which undue deformation may occur, for example, during relative axial movement between the seal 10 and the first machine component 18, the two surfaces 26 and 28 which lead up to the cornice 16 are conventionally located and configured to define an obtuse angle therebetween. Such a configuration, while providing adequate resistance against undue deformation of the lip 14, results in a less-than-optimal interface angle between the upstream surface 26 of the lip 14 and the surface of the first machine component 18 and, thus, may not be entirely effective in piercing the fluid film formed on the surface of the first machine component 18.
In view of the shortcomings in the art, it would be advantageous to provide a lip seal which provides increased contact force at its interface with a relatively moving machine component while possibly reducing the area of contact between the seal and the relatively moving machine component. It would further be advantageous to provide such a seal wherein a reduced-radius contact surface may be formed at a desired interface angle with respect to the relatively moving machine component while providing stability for such a contact surface.